Ecology
What's covered
Key facts
Biodiversity
Higher biodiversity makes ecosystems more stable because redundancy means other species can fill lost ecological roles.
Biomass and Energy Transfer
Biomass decreases at each higher trophic level because energy is lost as heat, movement, and undigested faeces.
Biotic and Abiotic Factors
Abiotic factors are non-living environmental factors: light intensity, temperature, water/ moisture, oxygen concentration, soil pH, and mineral content.
Conservation
Captive breeding programmes breed endangered species in zoos or reserves to increase population numbers and reintroduce individuals to the wild.
Ecosystems
Examples of abiotic factors include temperature and light intensity.
Food Chains and Food Webs
An arrow in a food chain represents the direction of energy and biomass transfer.
Human Impacts on Ecosystems
Acid rain lowers the pH of lakes and rivers, killing fish and aquatic invertebrates.
Nutrient Cycles
Combustion of fossil fuels adds carbon dioxide to the atmosphere.
Predator-Prey Relationships
The classic Arctic-Canada example of predator-prey cycling is lynx and (snowshoe) hare.
Sampling Ecosystems
A belt transect investigates how organism distribution changes across an environmental gradient.
Sample questions
A taste of the 129 questions in this topic, answers marked. Sign up to practise the full set with spaced repetition.
What is biodiversity?
- •The geographic range of one species across many habitats.
- •The rate at which new species evolve in an area.
- •The total number of individuals in a single species.
- ✓The variety of species in an ecosystem, supporting stability.
Why is biomass less at each higher trophic level?
- ✓Energy is lost as heat, movement, and undigested faeces.
- •Energy is stored in soil between each trophic level.
- •Higher animals are bigger and need less food per kilogram.
- •Producers convert all sunlight into biomass at the base.
Which is an abiotic factor?
- ✓Air temperature
- •Disease outbreak
- •Food competition
- •New predator
Which methods can humans use to protect endangered species?
- •Adding more predators and banning tourism in protected areas.
- ✓Captive breeding, seed banks, reserves, and reintroduction programmes.
- •Removing native species and using fertilisers to boost growth.
- •Restricting photosynthesis to reduce plant competition for animals.
What is the difference between a community and an ecosystem?
- •A community contains only animals; an ecosystem adds plants too.
- •A community is larger than an ecosystem in its scope.
- •An ecosystem has been studied; a community is unstudied.
- ✓Community is all living organisms; ecosystem adds the abiotic environment.
What does an arrow in a food chain represent?
- ✓Direction of energy and biomass transfer
- •Direction of evolutionary change
- •Direction of predator movement
- •Direction of waste excretion
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